Pulmonary drug delivery is an attractive alternative to oral, transdermal, and parenteral administration because self-administration is simple, there is no first-pass liver effect of absorbed drugs, and there is reduced enzymatic activity and pH-mediated drug degradation associated with the oral route. Furthermore, structural and physiological features of the lung, including a large mucosal surface and intricate branching for drug absorption, make aerosolization a desirable method for delivering therapeutic agents to the lung.
The mammalian respiratory tract can be divided into the upper airways, including the oropharynx, larynx and trachea; the central airways, including the bronchi and bronchioli; and the deep lung, including the alveoli. The lung is the site of many severe, chronic, life-threatening diseases such as chronic bronchitis, asthma, emphysema, lung cancer, and persistent pulmonary infections of various origins.
Several conventional pharmaceutical therapies for pulmonary diseases could be supplanted by gene transfer therapies. For example, studies have been conducted to assess the feasibility of gene therapeutic approaches to treating cystic fibrosis (CF) to correct deficiencies in the CFTR protein (McDonald et al. (1997) Hum. Gene Ther. 8:411–422; and Porteous et al. (1997) Gene Therapy 4:210–218); emphysema associated with α1-antitrypsin deficiency (Rosenfeld et al. (1991) Science 252:431–434; Canonico et al. (1994) Am. J. Respir. Cell. Mol. Biol. 10:24–29; and Knoell and Wewers (1995) Chest 107:535–545); oxygen injury (Erzurum et al. 91993) Nucl. Acids Res. 21:1607–1612); lung cancer (Smith et al. (1994) Hum. Gene Ther. 5:29–35; and Fujiwara et al. (1994) J. Natl. Cancer Inst. 86(19):1458–1462); and general inflammatory pulmonary conditions (Kolls et al. (1995) J. Infect. Dis. 171:570–575; and Brigham et al. (1994) Prog. Clin. Biol. Res. 388:361–365).
In vivo systemic expression of genetic material introduced into the respiratory tract has also been used to provide therapeutically effective levels of a secreted cytokine. Cannizzo et al. ((1997) Nature Biotechnol. 15:570–573) administered an adenovirus vector, containing a human thrombopoietin cDNA under control of a CMV promoter, into the trachea of BALB/c mice. Within a week after treatment, human thrombopoietin was seen in the serum, platelet levels increased over six-fold, and megakaryocytosis was seen in the bone marrow.
Another therapeutic approach involving polynucleotide administration is the generation of an immune response in the absence of a viral vaccine. Introduction of expression vectors into animals generates an immune response to the expressed protein. U.S. Pat. No. 5,589,466. This technique is useful, for example, where a viral vaccine is difficult to produce, or a nonpathogenic strain of the virus is not available. Administration of such expression vectors to the lung can yield immune responses without the disadvantages associated with injections, and may be directed to pathogens affecting the respiratory tract such as influenza virus, respiratory syncytial virus, hantavirus or adenovirus, and respiratory tract disorders such as asthma. Expression vectors can also be used to induce immune tolerance. U.S. Pat. No. 5,849,719.
Delivery of various therapeutic agents, particularly macromolecules, to the respiratory tract has proved challenging. Some of the difficulties encountered include excessive loss of inhaled drug in the oropharyngeal cavity, phagocytosis by lung macrophages, and poor control over the site of deposition. Selective delivery into various parts of the respiratory tract by “focal” methods such as microspray into limited anatomical regions (e.g., nasal or oral cavity, selected airways) has been attempted. Patapoff and Gonda (1997) in “Inhalation Delivery of Therapeutic Peptides and Proteins”, A. Adjei and P. Gupta, eds., Marcel Dekker, Inc. Other methods include endotracheal catheterization (U.S. Pat. No. 5,803,078). To date, however, no method has been shown to be adequate for the reproducible delivery of polynucleotides to specified portions of the respiratory tract. In addition, delivery to the lung of polynucleotide therapeutics has proved more difficult than delivery of small molecule therapeutics, in part due to the larger size of polynucleotides and their greater susceptibility to physical disruption from the forces required to generate an aerosol, thereby hindering or preventing efficient therapy.
There is currently a need for improved methods for delivery of polynucleotides to particular regions of the mammalian respiratory tract. The current invention addresses these needs and provides related advantages as well.